The invention relates to an alloy which is useful as an infiltration binder for bonding diamond cutting elements to a matrix body. More particularly, the invention relates to a low melting point copper-manganese-zinc alloy that is useful as an infiltration binder to bond diamond or other superhard cutting elements to a matrix body, such as a matrix drill bit body. The invention also relates to a process for producing a coherent matrix body by infiltrating a matrix powder with the new low melting point copper-manganese-zinc alloy.
The invention described herein is especially useful for the manufacture of rotary drill bits of the kind comprising a bit body having an external surface on which are mounted a plurality of cutting elements for cutting or abrading rock formations, and an inner passage for supplying drilling fluid to one or more nozzles at the external surface of the bit. The nozzles are located at the surface of the bit body so that drilling fluid emerges from the nozzles and flows by the cutting elements during drilling so as to cool and/or clean them. Desirably, the cutting elements are preformed cutting elements having a superhard cutting face formed of polycrystalline diamond or another superhard material.
As will be understood by persons skilled in the art, the term "superhard" is used to describe diamond and cubic boron nitride materials. For convenience, the term "diamond" is used herein interchangeably with the term "superhard" and is meant to include diamond (single crystal and polycrystalline) materials made at high or low pressure (metastable growth), as well as cubic boron nitride materials.
Drag bits for rock drilling are conventionally made by one of two methods. According to one conventional method, a steel body bit is made by machining a large piece of steel to the desired shape, drilling holes in the bit body to receive the diamond-containing cutting elements, and then pressing the diamond cutters into place. The diamond cutters are held in place mechanically by the interference fit of the cutters and the holes when the bits are made by this method. Alternately, the cutters can be brazed to the steel bit body.
According to the other conventional method of making drag bits, a matrix bit body is formed by a powder metallurgy process. U.S. Pat. No. 3,757,878 (Wilder et al) and U.S. Pat. No. 4,780,274 (Barr), which are incorporated herein by reference, are examples of the powder metallurgy used to produce matrix drill bits. In this process, a graphite block is machined to form a mold. A wear-resistant matrix powder, made for example from tungsten carbide powder particles, is placed in the mold, and a steel blank is inserted into the mold on top of the matrix powder. Thereafter, an infiltrating alloy is placed in the mold. When heat is applied, the infiltrating alloy melts and penetrates into the matrix powder to fill the interparticle space. Upon cooling, the infiltrating alloy solidifies and cements the matrix powder particles together into a coherent integral mass. The infiltrating alloy also bonds this coherent mass to the steel blank to form the matrix body bit. A threaded connection is then welded to the end of the steel blank to permit the bit to be attached to a drill string. The furnace temperature required to carry out this process with conventional copper-based infiltration alloys is about 1,065.degree. C. to about 1,200.degree. C.
The diamond-containing cutting elements are attached to a matrix drill bit made in this manner in one of two ways. If the diamond-containing cutters are capable of withstanding the infiltration temperature without substantial degradation, they are placed in the mold before the matrix powder is added and become bonded to the matrix body as a result of the infiltration process. The diamond-containing cutters become an integral part of the matrix drill bit. However, if the diamond-containing cutters cannot withstand the infiltration temperature without substantial degradation, the cutters are attached to the bit body, usually by brazing, after the infiltrated bit is removed from the mold.
Brazing the diamond-containing cutters to the body of the drill bit is less desirable than bonding the cutters directly to the matrix body during the infiltration process. Brazing is an extra step in the manufacturing process which has its own complications. While it would obviously be desirable to eliminate the brazing step in the manufacture of matrix drill bits, many of the diamond-containing cutting elements which are commercially available cannot withstand the infiltration temperatures that are needed with traditional copper-based infiltration alloys. For example, conventional polycrystalline diamond preforms are only thermally stable up to a temperature of about 700.degree. C. to 750.degree. C., and therefore must be brazed to the bit body after it has been infiltrated. More recent polycrystalline diamond preforms, e.g., Geoset.TM. preforms available from General Electric and Syndax 3.TM. preforms available from DeBeers, are nominally thermally stable up to conventional infiltration temperatures of about 1150.degree. C. However, in actual practice, the Geoset.TM. thermally stable polycrystalline diamond cutting elements begin to degrade at temperatures as low as 1000.degree. C. More recently, DeBeers has developed a polycrystalline diamond preform called STSR Syndrill.TM. which is thermally stable up to nearly 1000.degree. C.
As a result, there has been an intense search by persons skilled in the art for new infiltration alloys which have much lower infiltration temperatures than those of conventional copper-based infiltrants. U.S. Pat. No. 4,669,522 (Griffin) discloses an essentially two-element copper-phosphorous alloy of eutectic or near-eutectic composition as an infiltration alloy. The infiltration temperature of this alloy is disclosed as being not greater than 850.degree. C., and preferably not greater than 750.degree. C. However, there is reason to believe that this copper-phosphorous infiltration alloy has certain metallurgical problems associated with its use and therefore it has not met with great commercial success.
It is an advantage of the present invention that a new infiltrating alloy which has an infiltrating temperature below about 1000.degree. C. is provided.
It is another advantage of the present invention that a new method for the manufacture of coherent matrix bodies using an infiltration alloy having an infiltration temperature below about 1000.degree. C. is provided.
It is yet another advantage of the present invention that a method for producing matrix drill bit bodies with a copper-based infiltration alloy having an infiltration temperature below about 1000.degree. C. is provided.